ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

PROCEDURE

Step-1: Place the balance on a flat surface. Rotate the knob upon which the analytical balance rests to manipulate the mercury movement. Ensure that the mercury drop is within the circle, which indicates that balance is placed at symmetry.  view video

• Find out the weight of a clean dry silica crucible/basin. view video
• Place about 2 to 5 g of the sample and weigh this to find out accurate weight of the sample taken. view video
• Carefully place the weighed crucible/basin over electric Bunsen burner. The crucible should be partially opened. view video
• The sample will get charred with initial expulsion of smoke.
• Heat the substance gently to avoid catching fire by adjusting temperature of the burner. When the smoke subsides increase the temperature of the burner. view video
• Now the substance is gradually ashed. view video
• In case ashing is to be carried out only on Bunsen burner continue the heating till it is completely transformed into whitish ash. view video
• Place the balance on a flat surface. Rotate the knob upon which the analytical balance rests to manipulate the mercury movement. Ensure that the mercury drop is within the circle, which indicates that balance is placed at symmetry. view video
• If there is still black colour, it means further ashing is required.
• Switch off the burner, cool the crucible/basin  to room temperature preferably in a desiccator.
• Weigh the crucible/basin with its contents and record the weight. view video
• Again heat it to effect any possible ashing, cool and weigh. If there is difference, repeat this process till two consecutive weighings agree, there by indicating that complete combustion has taken place.

Muffle furnace

• Muffle furnace is electrically operated equipment used to ash substances. The temperature of muffle furnace can be raised up to 1000º C.
• In the above experiment after initial heating (i.e., after all the smoke has subsided) transfer the crucible/basin with its contents to muffle. Set the temperature to 600º C (the temperature will vary depending upon the purpose. If it is mere total ash estimation, the temperature can be as high as 600º C. But if you want to determine minerals like phosphorus very high temperature should be avoided ashing can be done at 400º C). Complete ashing will be effected in 5 or 6 hours.
• There is no need to repeat the process of heating and reweighing. However, open the muffle door only after the muffle temperature is below 100º C.

Calculation

• Weight of empty crucible - X
• Weight of crucible + sample - Y
• After complete ashing
• Weight of crucible + ash - Z

Calculation of organic matter

• Organic matter denotes the presence of carbon elements.
• It can be calculated by subtracting the inorganic part of the sample from 100.
  • Organic matter of fresh sample = 100 – (% moisture + % total ash)
  • Organic matter of dried sample = 100 – % total ash

Precaution

• The ash is highly hygroscopic and thus weighing should be done quickly